The present invention relates to a torque transmitting assembly adapted primarily for use as a torque transfer/spilt unit for use with four wheel drive and more than four wheel drive vehicles, as a differential unit, or as a limited slip differential unit.
JP 60-116529 discloses a torque transmitting assembly which comprises a rotary input member including a rotor, a rotary output member including a cam ring surrounding the rotor. The rotor and the cam ring cooperate with each other to form a conventional vane pump. The vane pump is associated with a hydraulic circuit. When differential rotation occurs between the rotor and the cam ring, the vane pump produces hydraulic pressure having a magnitude variable with the differential rotation, causing a ratio of input torque from the rotor to be transmitted to the cam ring. This ratio is variable with the magnitude of the hydraulic pressure produced by the vane pump and the effective pressure acting areas of the vanes. This known torque transmitting assembly has difficulty in obtaining a stable torque transmitting performance because the components, such as a relief valve and passageways, of the hydraulic circuit, are mounted in unitary rotation with the cam ring. Thus the hydraulic fluid in the passageways and the relief valve are subject to centrifugal force occurring when the cam ring rotates at high rotational speeds. That is, the hydraulic pressure produced by the vane pump is affected by the centrifugal force, thus causing a difficulty in designing the hydraulic circuit so as to minimize the centrifugal effect. Since the hydraulic circuit is rotatable with the rotary output member integral with the cam ring, the components of the hydraulic circuit need to be arranged so that imbalance of mass of the cam ring will be minimized. However, this is very difficult, so that the cam ring tends to vibrate when it rotates at high speeds. If the vane pump is used as a hydraulic pump of a torque transmitting assembly as is the case in the known torque transmitting assembly, it is difficult to transmit input torque to the cam ring until the differential rotation increases above a relatively high level because the sealing performance of the vane pump is so poor that a hydraulic pressure high enough for torque transmitting operation will not be produced when the differential rotation is small.
U.S. Pat. No. 3,577,803 (corresponding to JP 54-4134) issued to Mueller on May 4, 1971 discloses a torque transmitting assembly for use as a torque transfer/split unit for a four or six wheel drive motor vehicle. The torque transmitting assembly comprises a first rotary element. A second rotary element is coaxially disposed within the first rotary element. A rotary input member is journalled in a stationary housing and extends into the housing connected for rotation with the first rotary element. A second rotary output member is connected for rotation with said rotary input member. Hydraulic means normally couples the first and second rotary elements together and is operable under predetermined hydraulic pressure conditions to transmit a selected ratio of the input torque from the rotary input member to said first rotary output member with the remainder of the torque being transmitted from the input member to said second rotary input member. Selector means sets the predetermined hydraulic pressure conditions under which the hydraulic means will operate so as to set the ratio of torque transmitted to said output members. The first rotary element is formed with a plurality of radially inwardly opening pressure chambers facing the second rotary element. The second rotary element includes radially directed rise and fall cam surfaces. The hydraulic means includes pistons in said pressure chambers in engagement with the cam surfaces and reciprocable in response to differential rotation of the first and second rotary elements. The pistons and their associated chambers are in a plurality of sets. Passage means is in fluid communication with the chambers of each set, through which hydraulic fluid will flow from one set of chambers to another when the pistons reciprocate. A normally closed spring loaded ball check element is disposed in the passage means and prevents fluid communication between the sets of chambers when closed and, when open, regulates the rate at which fluid can flow between the sets of chambers. The selector means includes an adjustment element for selectively setting the spring-loading of the ball check element. When the ball check element is in a closed position, no fluid can be displaced from the sets of fluid pressure chambers, and therefore, no relative rotation occurs between the first rotary element and the second rotary element. However, when the ball check element is moved to an open position, hydraulic fluid displaced from the pressure chamber can be discharged through a port in which the ball check element is located. The extent of opening of this port will control the rate at which relative rotation can occur between the first and second rotary element. The hydraulic fluid that passes through the port in which the ball check element is located will be returned to the pressure chambers on the suction strokes of the pistons.
In this known torque transmitting assembly, since the ratio of torque transmitted to the output members is set by the ball check element operable by the selector means, so called tight braking phenomena will occur when a relatively small differential rotation need to occur between front wheels and rear wheels on turning on a road with a high friction coefficient if the ball check element is left in the closed position.
Since the radially directed rise and fall cam surfaces are formed on the second rotary element disposed radially inside the first rotary element, the circumferential distance between the high point of the cam surface and the adjacent low point thereof is not long enough to allow a mild and gradual cam slope to extend between the high point and the low point. This also causes a difficulty in finishing the surface of the slope. As a result, a high possibility exists that the associated pistons cannot follow the cam surfaces so that the pistons will impinge on the cam surfaces, thereby to allow production of sound due to such impinging.
Since the pistons are directed radially inwardly to rest on the radially outwardly directed cam surfaces of the second rotary element, the pistons loose their appropriate engagement with the cam surfaces due to the centrifugal force when the rotary elements rotate at high speeds. Thus, the ratio of torque transmitted to the second rotary element decreases as the vehicle speed increases.